1. Field of the Invention
The present invention relates to a system for controlling the air/fuel ratio and output of a naturally aspirated railroad locomotive in response to operation at barometric pressures characteristic of operation at varying altitudes. The present invention allows the smoke output of the locomotive to be controlled at changing altitudes.
2. Disclosure Information
Naturally aspirated railroad locomotives typically are powered by compression ignition “diesel” engines. Such engines may be either four-stroke cycle or two-stroke cycle engines. Four-stroke naturally aspirated engines have no charge air booster such as a turbocharger or a supercharger. Two-stroke cycle diesel engines used in railroad locomotives are typically scavenged with a positive displacement blower such as a Roots-type blower. Notwithstanding the use of blower scavenging, such engines typically operate in a manner similar to naturally aspirated engines because the Roots blower or other type of positive displacement blower merely serves to force exhaust gases from the engine's cylinders at a pressure only slightly above atmospheric pressure, with the result that the airbox supplying the engine cylinders or intake manifold operates very closely to ambient air pressure.
Naturally aspirated railroad locomotives are, of course, subject to operation at altitude, and at higher altitudes, say above 2500 feet, operation may be characterized by production of excessive exhaust smoke. This smoke results from the lack of oxygen at higher altitudes. Naturally aspirated locomotives are usually calibrated so that the engine powering the locomotive operates at one of eight notches characteristic of different engine speeds. Moreover, each notch is usually calibrated at a different air/fuel ratio, with notch 1, the lowest engine speed having the leanest air/fuel ratio or highest numerical air/fuel ratio, and notch 8 having the richest, or lowest numerical air/fuel ratio. It is easily seen that if a naturally aspirated locomotive is operated at high altitude at the higher notches, e.g., 6, 7 and 8, smoking may occur due to the richer fuel calibration at the higher notches, coupled with lack of oxygen availability.
It would be desirable to control air/fuel ratio with the engine operating system commonly used on naturally aspirated locomotives, so as to reduce the production of smoke when the engine is operated at higher altitudes.